Line Probe Assay [LPA] in DR-TB Diagnosis

As per the Integrated Drug-resistant Tuberculosis (DR-TB) Diagnostic Algorithm:

• Nucleic Acid Amplification Tests (NAAT) are preferred for the initial detection of Rifampicin (R) resistance
• Line Probe Assays (LPA) are preferred for the detection of Isoniazid (H), Fluoroquinolones (FQ) and second-line injectable (SLI) drugs resistance.

When rifampicin resistance is detected by NAAT (see figure below):

• Offer first-line (FL) and second line (SL) LPA
• Direct LPA performed on smear positive specimen or indirect LPA is performed on culture isolate when the smear is negative

When Rifampicin resistance is not detected by NAAT (see figure below):

• Offer FL LPA to detect H resistance
• Direct LPA performed on smear positive specimen or indirect LPA is performed on culture isolate when the smear is negative
• If H resistance is detected; SL LPA is performed to check FQ resistance

Figure: Flowchart to decide FL/SL-LPA after NAAT results

Resources

• Guidelines for PMDT in India, 2021.​
• GLI LPA Guidance Document.

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